Complex europium salt

ABSTRACT

A COMPLEX OF A EUROPIUM SALT, SOLUBLE IN ACIDIC AQUEOUS MEDIA, IS PROVIDED IN THE FORM OF EUROPIUM TRICHLORIDE COMPLEXED WITH A DIPOLAR APROTIC SOLVENT OF THE TYPE EXEMPLIFIED BY N,N-DIMETHYLFORMAMIDE, N,N-DIMETHYLACETAMIDE, METHYL SULFOXIDE, AND N,N,N&#39;&#39;,N&#39;&#39;N&#39;&#39;&#39;&#39;,N&#39;&#39;&#39;&#39;-HEXAMETHYLPHOSPHORAMIDE.

United States Patent Olhce 3,646,080 COMPLEX EUROPIUM SALT HarveyPobiner, Princeton, N.J., assignor to American Can Company, New York,N.Y.

No Drawing. Original application June 14, 1967, Ser. No. 645,896.Divided and this application May 12, 1969, Ser. No. 835,859

Int. Cl. C07f /00 US. Cl. 260-4292 1 Claim ABSTRACT OF THE DISCLOSURE Acomplex of a europium salt, soluble in acidic aqueous media, is providedin the form of europium trichloride complexed with a dipolar aproticsolvent of the type exemplified by N,N-dimethylformamide,N,N-dimethylacetamide, methyl sulfoxide, andN,N,N,N',N,N"-hexamethylphosphoramide.

3,646,080 Patented Feb. 29, 1972 E1120; GNaCl 8HCN(OH or TABLEI.-SUMMARY OF THE REACTIONS OF THE RARE EARTH METALS IN ADIMETHYLFORMAM'IDE (DMF)-HYDROCHLORIG ACID SYSTEM Atomic Oxide Rareearth metal No. used Result of H01 plus DMF complexation Yttrium 39 YgOQInsoluble oxide. Lanthanum 57 La O Homogeneous solution, no UV maximum.

68 CeO, Insoluble oxide. 59 PraOn D0. 60 Nd 03 Homogeneous solution, noUV maximum. 62 Sm 0 D0. 63 Eu o Homogeneous solution, UV maximum,268

mu. Gadolinium 64 GdzO3 Homogeneous solution, no UV maximum. Ierbium 65'IblOq Insoluble oxide. Dysprosium- 66 Dygoa Homogeneous solution, no UVmaximum. Holmium- 67 H0 0 Do. Erbium. 68 Er O Homogeneous system, no UVmaximum. Thulium 69 T111203 Insoluble oxide. Ytterbium. 70 Yb O Do.Lutetium 71 1111203 Do.

1 Element 61, Promethium, is a radioactive decay product of uranium.Since it is not a naturally occurring rare earth metal, it Was omittedfrom the investigation.

This application is a division of my application Ser. No. 645,896, filedJune 14, 1967, now Pat. No. 3,468,622.

This invention relates to achieving recovery of one or more rare earthmetal values from mixtures containing same.

It will be appreciated that the rare earth compounds are well named inthat they are rare, indeed, and therefore quite expensive. The matter isdoubly compounded by the fact that the rare earth salts are either foundin combination in nature or used in combination so that they areseparated with difiiculty, since they possess relatively similarreaction characteristics.

The general concept of the present invention relies on the recovery ofeuropium oxide from rare earth mixtures, phosphors and photoresponsivematrices. Naturally, the remainder, after removal of the europiumcompound, may be used in further recovery techniques.

In carrying out the concept of the invention, the europium oxide iscomplexed after acidification, for instance, with hydrochloric acid,with a dipolar aprotic solvent such as dimethylformamide,dimethylsulfoxide, hexamethylphosphoramide and dimethylacetamide. Byremoving the undissolved solids by filtration and the like, theremaining filtrate contains the complexed europium compound. The key tothe process of recovery of the europium oxide from the complex isachieved by rendering the system alkaline. The following equationsapply:

Euro GHGI 2EuCl 3Hz0 The recovery of europium oxide depends on thealkaline decomposition of the complex EuCl DM'F. Further, the degree ofthe decomposition is a function of alkalinity. Also, since the complexproduces an ultraviolet absorption spectrum unique among the rare earthoxides, this spectrum serves as a measure of the complexed europiumoxide in solution. As the pH is adjusted from 1.0 (the pH of theinitially complexed solution) to pH 10.5 (the pH at which the Eu O iscompletely out of solution), the intensity of the ultraviolet absorptionmaximum changes significantly. This is shown in Table H. It will beobserved that it is necessary to reach a pH 10.5 for quantitativerecovery of Eu O when complexing with DMF.

TABLE II.-RECOVERY O'li E1120; FROM EuC*la-DMF AS A FUNCTION OF pHPercent Eu 0 UV absorption remaining as coetfieient, complex in K 268my. 1 solution While the processes as set forth in the examples have aunifying thread running therethrough, the methods are not completelyidentical. Some changes should be made to take into account the materialfor salvage. Of course, fundamental in each example is the conversion ofthe europium oxide to its salt and the complexation with a dipolaraprotic solvent, usually carried out at room temperature. When adjustedto pH 10.5, the europium oxide flocculates and is recovered byfiltration and the like. In those instances when yttrium is present inthe to-be-treated mixture, a mixed oxide fraction is recovered at pH6.5, prior to an alkalinization to pH 10.5. This results in a cleanerseparation of the two rare earth oxides. On the other hand, theinsolubility of terbium oxide, Tb407, allows for complete separationfrom the recovered B11203 and a single pH 10.5 fraction sufiices forrecovery. Europium oxide is similarly separated from a barium titanateceramic and from an alumina matrix which are initially ground intopowder.

When zinc oxide matrix is involved, the separation of europium oxide isdependent on the use of ammonium hydroxide in separating out at a pH10.5. Caustic cannot be used in such an instance as the zinc hydroxideformed is gelationous which would contaminate the recovered Eu O Byusing ammonium hydroxide, the problem is obviated.

While usually the most efficacious acid is hydrochloric acid, othermineral acids are applicable such as sulfuric and nitric. Furthermore,the acid selected should not attack the dipolar aprotic solvent. Someorganic acids, such as acetic acid, are applicable in carrying out theacidulation step.

The amount of the dipolar aprotic solvent to be most efiicient is aboutfour moles to every mole of theoretically available europium value. Ofcourse, if one or more of the other rare earth values, such as in thecase of yttrium compound, is to be complexed, followed by distinctalkalinization steps, it will be necessary to take into account theoverall quantity of the dipolar aprotic solvent necessary.

The following examples are set forth to give further illustration of theconcepts of the present invention.

EXAMPLE I This example is presented to illustrate the concept of thepresent invention in regard to the separation of europium oxide from aphosphor containing both yttrium oxide and europium oxide. Theseparation is predicated on the relative insolubility of the yttriumoxide in a dimethylformamide-hydrochloric acid solvent system thatselectively complexes the europium oxide.

In carrying out the example, for ecah gram of the Y O -Eu O phosphor,the following are added to the reaction vessel: 25 ml.dimethylformamide, 5 ml. of wt./vol. sodium chloride aqueous solution, 3ml. of 37% hydrochloric acid, and 10 ml. of distilled water. Theresultant mixture is stirred for two hours. The undissolved material isyttrium oxide and the former europium oxide is in solution as theeuropium chloride-dimethylformamide complex.

The mixture is filtered to thereby remove the undissolved materials. Thefiltrate which contains the complex, and a relatively small quantity ofyttrium oxide, is adjusted in pH to 6.5 with 10% solution of sodiumhydroxide. The resultant is heated to encourage the formation of afilterable precipitate which is the remaining yttrium oxide and a smallquantity of Eu O .6H O.

The initial Y O fraction separated represents 86% of the original Y O inthe mixture, the remaining 14% Y O is in the mixed oxide phase, that is,the precipitate produced when the pH is adjusted to 6.5, in the above.The final Eu O fraction represents 89% of the original Eu O with theremaining 11% of the Eu O in the mixed oxide phase.

EXAMPLE II The present example deals with the separation of europiumoxide from a mixture comprising terbium oxide and europium oxide.

The mixture of Tb O and Eu O is separated and recovered in a techniqueas in Example I, except that the intermediate alkalinization to the pH6.5 level is not necessary due to the insolubility of'Tb O in thesolvent system. It is only necessary to recover the Tb O which remainssoluble as the oxide while the Eu O is not precipitated until thefiltrate containing the complex is adjusted to a pH of 10.5. By thissystem, 96% of the original Eu O is recovered and 97% of the original TbO is recovered.

EXAMPLE III In this example, europium as the oxide is recovered from aphosphor containing europium oxide and barium titanate.

The mixture is usually a ceramic matrix which must be ground into apowder. For each one gram of the ceramic powder in a 250 ml. beaker 25ml. of dimethylformamide, 5 ml. of 15% wt./vol. solution sodium chlorideand 3 ml. of 37% hydrochloric acid and 10 ml. of distilled water areadded. The resultant is agitated for two hours at room temperature. Thenthe insolubles are filtered out. The solids represent barium titanate.

The filtrate is adjusted to a pH of 10.5 with 10% solution of sodiumhydroxide in order to decompose the euro pium chloride-dimethylformamidecomplex. The europium oxide precipitates. The resultant mixture isheated to coagulate the europium oxide and is allowed to stand for abouttwo hours.

The solids are then recovered by filtering and are then washed. Thesesolids are dried at 200 C. for two hours and represent the recoveryeuropium oxide as the hexahydrate. It is possible by this example torecover 97.8% of the barium titanate and 99% of the europium oxide.

EXAMPLE III-A In the foregoing it was stated that under some conditionsan organic acid, such as acetic acid, would be effective as a mineralacid, such as hydrochloric acid.

To illustrate the etficacy of employing acetic acid, the procedure ofExample III is utilized except that acetic acid in the same mole ratiois substituted for the hydrochloric acid. A 15% sodium acetate solutionis substituted for the solution of sodium chloride. It is necessary tosubstitute a heating step at C. for 30 minutes for the two-houragitation period of Example III. It is also necessary to undertake aplurality of successive recrystallizations to obtain a good yield of EuO that is, in this example 98.5%.

Due to the need for a heating step and requirement that severalrecrystallizations be undertaken before a satisfactory Eu O yield isobtained, clearly the more useful acids will be the inorganic acids,such as hydrochloric acid.

EXAMPLE IV The method of this example is the same as in connection withExample III except that the mixture is Eu O Al O phosphors. By applyingthe method, 99.3% of the aluminum oxide is recovered and 91% of theeuropium oxide is recovered.

EXAMPLES V AND VI In this method, europium oxide is recovered fromphosphors of calcium tungstate (Example V) and calicurn molybdate(Example VI). The process is carried out as in Example III. In thisseparation, the tungstate is recoverable to a greater degree than is themolybdate. Between 8994% of the original Eu O is recovered from themolybdate and tungstate matrices after a single recrystallization.

EXAMPLE vrr In this method, europium oxide is recovered from a zincoxide matrix.

For each one gram of the zinc oxide matrix, the following are added: 25ml. dimethylformamide, 5 ml. of 15% wt./vol. solution of sodiumchloride, 3 ml. of 37% hydrochloric acid and ml. of distilled water. Themixture is stirred for two hours at room temperature. A true solution isobtained. This solution is rendered alkaline to a pH of 10.5 withammonium hydroxide. As a result, europium oxide flocculates andprecipitates from the solution. By using ammonium hydroxide instead ofthe sodium hydroxide, the zinc stays in solution; with sodium hydroxidethe zinc hydroxide forms a gelatinous precipitate.

After pH adjustment, the mixture is heated to below boiling andpermitted to be in a quiescent state for at least two hours. The solidsare then recovered by filtration and washed with water. They are thendried at 200 C. for two hours and recovered as Eu O -6H O. 92-95%recovery of the original europium oxide present is realized by employingthis technique.

EXAMPLES VIII AND IX In this method, europium oxide is recovered fromphosphors of cadmium sulfide (Example VIII) and zinc sulfide (ExampleIX). The process is carried out as in Example V, that is, the mixture isrendered alkaline with ammonium hydroxide. In other words, the zinc andcadmium remain in solution as the hydroxide and the europium oxide isliberated by alkaline decomposition of the europium complex. Afterrecrystallization, between 89- 91% of the original Eu O is recoveredfrom the phosphor.

EXAMPLE X The process of this example pertains to recovery of europiumoxide from a soluble borate matrix. The separation of europium oxidefrom a matrix or glass of sodium borate is facilitated by the solubilityof the sodium tetraborate in an alkaline medium and the recovery of Eu Ofrom the dimethylformamide complex at pH 10.5.

To each gram of the borate matrix to be treated, the following areadded: 25 ml. dimethylformamide, 5 ml. of wt./vol. solution of sodiumchloride, 3 ml. of 37% hydrochloric acid and 10 ml. of distilled water.Inasmuch as the borate is soluble, a true solution results after aperiod of stirring. Then, the pH is adjusted to 10.5 with solution ofsodium hydroxide. The mixture is The ligand dimethylsulfoxide is moreeificacious in this example than the dimethylformamide. While both ofthese rare earth oxides form homogeneous solutions withdimethylsulfoxide-hydrochloric acid solvent system, the europium oxidecan be recovered from its complex with dimethylsulfoxide-hydrochloricacid by adjusting the pH for alkaline decomposition to pH 8.0. At pH8.0, most of the neodymium oxide does not flocculate nor precipitatefrom the solution. At pH 8.5, Nd O begins to flocculate. By employingrecrystallization techniques, the europium oxide may be purified.

Specifically, applying the instant technique, for each one gram of theEu O -Nd O mixture, the following are added: 25 ml. dimethylsulfoxide, 5ml. of 15 wt./ vol. solution of sodium chloride, 3 ml. of 37%hydrochloric acid and 10 ml. of distilled water. The mixture is heateduntil a relatively clear solution is presented. The solution is thencooled to room temperature and the pH is carefully adjusted withrelatively dilute aqueous ammonium hydroxide to pH 8.08.1. As a resultthereof, the europium oxide flocculates as the 1 men, 4onah orn complexdecomposes. The neodymium compound as its complex remains in solution.Thereafter, the mixture is heated to near boiling, allowed to stand atroom temperature for two hours. At the end of this time, the solids arefiltered out and are washed, prior to recrystallization, to purify theeuropium oxide which is present, after drying, as the hexahydrate.

In a mixture of Eu O Nd O (49.l%50.9%, respectively), the firstrecrystallization produces a fraction of Eu O Additionalrecrystallization is required to obtain greater purity.

The importance of selecting dimethylsulfoxide DMSO as the ligand overdimethylformamide (DMF) in effectively separating europium oxide fromneodymium oxide is demonstrated in Table III.

TABLE III Oxide Ligand pH Percent removed MF 10.5 92-99% 1211,03. DMSO8.0 81% E1120... DMF 80 27% Ndg03. DMSO 9.4 87% Md203. 49 17 E o 1 DMSOi 7 iiii 1 u 3 8. o e origina 50.1%? NdZO; 1 1511,03.

1 Mixture of Example XI.

The following table summarizes the above examples,

heated to bollmg accompamed with stirring. After heat- 50 Clearlyillustrating the etficiacy of the instant invention.

TABLE IV Percent Percent by E11 0, Percent remaining Example Mixtureweight recovered component I Eu 03/Y2O3 29. 4l70.6 88.8 85.8. EuOa/Tb401 23.8/76.2 96.0 97.3. Eu oa/Baliog 16.4/83.6 99.3 97.8.

mos/A1 03 18.6/81.4 90.7 99.1 Eu O /CaWO4 8.6/9L4 194.4 96.4. E11 O/CaMoO 93/907 88.8 62.2. Eu203/Zl10 9.1/90.9 92.5 ZnO not recovered.EllgOa/CEIS 9. 2/90.8 88.7 OdS not recovered. Eu O /ZnS 10.6/89.4 90.6ZuS not recovered. EugOij/N32B401 15.9/84.1 99.0 Na B4O not recovered.XI Eu OaINd Oz 49.1/50.9 73.0 Nd O not recovered.

1 Recrystallization.

ing, the mixture is left to stand for at least two hours at roomtemperature. The solids are then recovered by filtration and washed. Thewashed solids are dried at 200 C. for two hours and recovered as Eu O-6H O. 99% recovery of the original europium oxide is realized in usingthe technique of this example.

EXAMPLE XI In this example, a technique is illustrated for recoveringeuropium oxide from a mixture of europium oxide and neodymium oxide.

It is therefore apparent that the foregoing description is by way ofillustration of the invention rather than limitation of the invention.

1 claim:

1. A complex of a europium salt, comprising europium chloride complexedwith a dipolar aprotic solvent selected from the group consisting ofdimethylformamide, dimethylacetamide, dimethyl sulfoxide, andhexamethylphosphoamide.

References Cited UNITED STATES PATENTS 3,049,403 8/ 1962 Krumholz 23-223,077,378 2/1963 Peppard et a1. 2323 3,089,758 5/1963 Kruesi 23-223,089,759 5/1963 Bronaugh et a1 2322 3,092,449 6/ 1963 Bril et a1 23223,153,571 10/1964 Bronaugh 2322 3,203,968 8/1965 Sebba 260-4292 8 OTHERREFERENCES Popov et al., The Methylamine Complexes of the Rare EarthChlorides, Jour. Amer. Chem. Soc., vol. 77, No. 4, Feb. 20, 1955, pp.857-859.

Moeller et al., Observations on the 'Rare Earths- LXXllI, Journal ofInorganic Nuclear Chemistry, vol. 15, pp. 259-264, 1960, Pergamon PressLtd.

Moeller et al., Observations on the Rare Earths- LXXVII, J. Inorg. Nucl.Chem, vol. 27, pp. 1477-1482, 1965, Pergamon Press Ltd.

BENJAMIN R. PADGETT, Primary Examiner F. M. GI'ITES, Assistant ExaminerUS. Cl. X.R.

